The present invention relates to fiber optics, and in particular to techniques for polishing fiber optics toward their core to access the evanescent field of the optical energy transmitted therein.
Fiber optics are becoming well known and used transmission media, as they can carry high bandwidth information using low-power optical energy. Like their well known electrically conductive counterparts (wires, cables, etc.), fiber optic circuits must also employ devices such as filters, modulators, amplifiers and attenuators. Techniques have been proposed by the present assignee, among others, for accessing the evanescent field of the optical energy transmitted in a fiber optic to perform the requisite filtering, modulation, amplification, attenuation, etc. These techniques involve removing a portion of the cladding of the fiber optic, close to the core, thereby exposing the evanescent field thereof. Using various controllable refractive index materials, applied over the exposed surface, which interact with the evanescent field, the optical energy transmitted in the fiber can be filtered, modulated, amplified, attenuated, etc.
One exemplary approach for polishing the fiber and accessing the evanescent field is disclosed in the co-pending U.S. patent applications Ser. Nos. 08/786,033, and 08/785,871, entitled xe2x80x9cElectro-Optic Compound Waveguide Modulatorxe2x80x9d and xe2x80x9cCompound Optical Waveguide and Filter Applications Thereof,xe2x80x9d both commonly assigned with the present application, and incorporated herein by reference in their entirety. In those applications, a grooved radius block is employed within which an unpolished fiber is placed. The fiber is polished using the block as a surrounding support structure, and the block/polished fiber assembly as a whole forms part of the eventual device (e.g., filter, modulator, etc.).
More particularly, a supporting glass block is initially prepared with a narrow (typically 130 xcexcm) channel cut with a constant radius of curvature. The optical fiber is stripped (i.e. any buffers removed), placed in the groove and permanently fixed therein with epoxy. The block-fiber assembly is then mounted to a polishing fixture, and both the block and fiber are simultaneously lapped and polished to approach/expose the core. This permits access to the evanescent optical field for processing (e.g., filtering modulation, amplification, attenuation, etc.).
There are several reasons for using this technique, including: (I) the need to mechanically support the fiber during the polishing process, and/or the subsequent device; and/or (ii) the need to maintain a large area planar coupling surface upon which to deposit an overlay material. This approach, although necessary for certain applications, especially for overlay waveguide coupling, has several limitations. Foremost of these is the difficulty of multiple fiber processing as a result of the inability to uniformly produce multiple grooves using standard cutting techniques. This limits the production rate of these devices, e.g., typically only one device can be processed per polishing fixture at a time. In addition, the glass block makes the device significantly larger, of much greater thermal mass (i.e., the block may operate as an undesirable thermal sink in a thermo-optic device), and more complicated to produce (i.e., both lapping and polishing steps are usually required).
In a concurrently-disclosed device, the support block is eliminated to improve performance, reduce the size and/or lower the cost of the device. (See the concurrently-filed, above-incorporated U.S. Patent Application entitled xe2x80x9cBlockless Fiber Optic Attenuators and Attenuation Systems Employing Dispersion Controlled Polymers.xe2x80x9d) In that application, an attenuator is disclosed in which the polished fiber optic is suspended in the support structure and is only contacted by a thermo-optic material. The remaining surrounding material (e.g., air) is thermally insulative, which is a characteristic that cannot be obtained using the polished block approach discussed above.
What is required are improved techniques for processing fiber optics, without the performance, size, weight, quantity or cost constraints associated with the block techniques.
The shortcomings of the prior fiber polishing approaches are overcome by the present invention which in one aspect relates to a method for removing material from multiple fiber optics, including providing an at least partially rounded surface; temporarily affixing portions of the fiber optics to the surface; polishing material from the portions of the fiber optics; and removing the fiber optics from the surface.
The fibers may be temporarily affixed, side-by-side, onto the surface. Preferably, a cylindrical surface (e.g., lens) is used and the fiber optics are aligned perpendicular to a longitudinal axis of the cylindrical surface. The surface may also be leveled, at least along this axis, before polishing.
During polishing, the polishing depth can be periodically checked using an optical loss power measurement. This may include placing a material over the polished surface (e.g., oil); transmitting optical energy through the fiber at a known power; and optically measuring an amount of the optical energy lost to the oil.
A related apparatus is also disclosed for facilitating the polishing of multiple fiber optics, which includes a partially rounded surface on which the multiple fiber optics are temporarily affixed, for polishing.
The xe2x80x9cblocklessxe2x80x9d processing techniques of the present invention provide benefits over the prior xe2x80x9cblockxe2x80x9d techniques, including reduced size and weight (and therefore thermal mass), reduced cost, and the ability to simultaneously process multiple fibers.